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Topic: Basic Yeast Questions (Read 7019 times)

I think I've been under pitching. As you know I bought a couple stir plates recently and I'm learning about that. I bought the Mr Malty app and figured out how to work that. I've watched a few wyeast and white labs videos. ..

1. Lets say I run a 2000ml starter for 24 hrs, then put the flask in the fridge to settle the yeast. How long can it sit in the fridge before decant and pitch? Would 3 or 4 days have much effect?

2. When washing and repitching from a previous brew, how do you estimate and measure how much of that to pitch. A low tech method would be awesome. How long can the washed yeast last in the fridge? Can you use the same viability rates as the smack packs, like about 30% loss per month?

3. Generally speaking, how do ester and fusel production relate to fermentor temp and pitch rate?

I'm asking these questions to verify my understanding. Here's what I think.

1. I think a starter would be just fine in the fridge for a few days, but after a week or so you begin losing viability.

2. I think if you wash a yeast cake right away and keep it in the fridge, it's good for a few days before viability loss starts. I personally wouldn't use it as-is past a month. I think for an <1.060 ale I would use a half cup slurry. Double for a lager or high gravity ale.

3. I think that low pitch rate encourages growth and therefore less esters and more off flavors. High pitch rate increases ester, decreases off flavor except if your over pitch leads to Autolysis. I think fermenting at the low end of the yeasts temp range reduces esters but risks off flavors from poor fermentation. Fermenting at the high end increases esters but risks high fusel production.

I can't speak to 2 and 3, but I see know reason to put the starter in the fridge to settle the yeast. When I make my starters, I make them first thing in the morning and then pitch it at the end of the day (10-15 hour mark). You are going to swirl the yeast before dumping into the wort anyway. I usually make a 1.5 or 2 liter starter and have never had any issues.

1. I've left yeast in the fridge 2 days once before and didn't notice any difference from when I left in in there overnight or the same day. I don't think the difference in viability from 1 - 3 days makes much difference on a homebrew level. As mentioned by travjohn above, I don't always cool and decant my starters. It really just depends on the beer. If I'm making a lower gravity beer, I may decant. If it's a bigger, darker beer, I just throw it all in. I've done this each way with an American Wheat beer and I couldn't tell a difference.

2. Mr. Malty can help determine how much slurry from washed yeast to use. Select the "repitching from slurry" tab and I usually slide the "yeast concentration" slider closer towards the "Thick Yeas" side since I will decant most of the liquid. When I wash my yeast, I usually store it into 4 different mason jars which have ml readings making it easy to estimate the amount of yeast in each jar. Depending on how much I will be using over the next week or two, I will either take a jar and make a starter or just throw in 2 jars, which usually will have 40 - 60ml of yeast slurry. With Mr. Malty, play with the "Harvest Date" in the "Repitching from Slurry" section to see how time changes the viability of the slurry.

3. As far as I know, you are correct with pitch rates with ester/ fusel production. Less yeast increases the ester/fusel production along with more diacetyl, which depending on the beer is what you may want. Higher pitch rates is less ester/ fusel. Fermenting on the lower side of the temp scale I think does help reduce esters, but I don't think you risk off flavors from poor fermentation. You may risk stuck fermentation if it gets too low, but I don't think it throws off flavors other than maybe a less drier beer. Ferment too high and you are in danger of some bad fusel production for sure.

I don't consider myself a yeast expert, so please if I'm wrong with any of this feel free to correct me.

« Last Edit: June 08, 2013, 01:46:21 AM by thebigbaker »

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Jeremy Baker

"An escalator can never break: it can only become stairs. You should never see an Escalator Temporarily Out Of Order sign, just Escalator Temporarily Stairs. Sorry for the convenience." - Mitch Hedberg

Thanks for pointing out the repitch feature. Assuming I rack a beer and wash the yeast to repitch one week later, using the middle setting on concentration and trube percentage, it shows I need 100ml for a 1.060 ale. That's just shy of a half cup. So I guess my knowledge was right on that one. I'm learning from you guys!

Per Mr Malty, repitch is 95% viable new, 75% at a month, and 50% at two months, and 33% at three months. So about the same viability as a smack pack. Personally I won't be holding used yeast more than a couple weeks.

Bigbaker, current theory is less yeast decreases ester production, not increases it. Both Clayton Cone of Lallemand and Neva Parker of White have talked about that. The same enzyme is responsible for cell growth and ester production and wheit does one it doesn't do the other. So, when you pitch less yeast, the enzyme is bust with cell growth and ester production is reduced.

Bigbaker, current theory is less yeast decreases ester production, not increases it. Both Clayton Cone of Lallemand and Neva Parker of White have talked about that. The same enzyme is responsible for cell growth and ester production and wheit does one it doesn't do the other. So, when you pitch less yeast, the enzyme is bust with cell growth and ester production is reduced.

Thanks Denny, I just went back and looked at Neva's presentation PDF from last year and she does state that lower yeast count decreases esters and higher increases them. I could have sworn that I read on White Labs or Wyeast's website somewhere that esters increased with lower yeast pitch rates. To prove to myself that I wasn't crazy, I just went to each site and Wyeast does state the opposite, with lower pitch rate = increased esters and vice versa. http://www.wyeastlab.com/com-pitch-rates.cfm

I know Neva Parker's presentation was just last year (thanks AHA for putting these presentations online for those of us who couldn't make the conference!), so is the less yeast = less ester theory relatively new? I'll search and see what Clayton has to say on the subject.

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Jeremy Baker

"An escalator can never break: it can only become stairs. You should never see an Escalator Temporarily Out Of Order sign, just Escalator Temporarily Stairs. Sorry for the convenience." - Mitch Hedberg

Thanks for the links. Wonder why there is different opinions w/ Wyeast stating that lower pitch rates = increase ester production and others are stating the opposite. Maybe I'll email Wyeast to explain their view and present to them some of the opposing views on this issue.

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Jeremy Baker

"An escalator can never break: it can only become stairs. You should never see an Escalator Temporarily Out Of Order sign, just Escalator Temporarily Stairs. Sorry for the convenience." - Mitch Hedberg

I checked my copy of Chris White's "Yeast" since Wyeast came up. He says in the book-1. Storage up to two weeks is probably best. The sooner the better. Made sense to me.2. From page 121, under pitching effects flavor more and over pitching has a bigger impact on health. It all apperears relative, though, because both over/under pitching can effect flavor with high levels of diacetyl and acetlaldehyde.His biggest point, IMHO, is when says to measure your yeast best you can, find what works with your beer and then be consistent.

Trying to be consistent was probably the only point that made sense to me.

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Whenever you find yourself on the side of the majority, it is time to pause and reflect.Mark Twain